Systematic physical activity has long term, positive health benefits for children that persist into adulthood. We propose that exercise treatments will improve children's cognitive functioning, particularly their executive function processes. In Experiment 1, we will assess children's cognitive performance using specific measures of mental processing (Cognitive Assessment System) prior to and immediately after a four-month after-school aerobic exercise training program to determine whether regular (chronic) physical activity has a salutary effect on cognitive functioning. Children will be assigned randomly to one of three groups: two levels of supervised exercise training (low and high dose; 20 and 40 min/d, each at an average heart rate >150 bpm) and a non-exercise control condition. Thus, we will determine possible dose-dependent effects of aerobic exercise training on children's cognitive functions. We will also explore possible related effects on behavior and attentiveness in class (Conners Rating Scales) and academic achievement (Woodcock- Johnson III). In Experiment 2. We will determine, using a computerized laboratory task, the impact of a single bout of steady state aerobic exercise on children's information processing. Experiment 2 will be conducted with children who have just completed the four-month exercise intervention period in Experiment 1, either as experimental or control subjects; thus, we will be able to determine if the acute impact of a single moderate exercise bout (equivalent to a brisk walk) on a child's information processing is influenced by the child's level of habitual physical activity. We hypothesize that the magnitude of change in information processing engendered by a bout of physical activity will be related to the treatments assigned to children in Experiment 1, such that those children who were assigned to the exercise classes in Experiment 1 will show a dose-response advantage on the Experiment 2 task (information processing following a bout of exercise), compared to the Experiment 1 control group. If we find that the 20 min/d dose of aerobic activity is effective in improving cognitive functioning in obese children, then a public health intervention optimizing physical education, health education, and opportunity for physical activity (e.g. recess) in schools might conceivably be sufficient to enhance children's academic performance. If 40 min/d are required to improve children's cognitive function, then larger-scale interventions, such as community, lifestyle and after-school physical activity programs may also be necessary to promote cognitive development.